Method of purifying catalysts



United States Patent 2,851,427 1 METHOD OF PURIFYING CATALYSTS George G.Joris, Princeton, N. J., assignor to the United States of America asrepresented by the United States Atomic Energy Commission No Drawing.Application March 22, 1945 Serial No. 584,254

3 Claims. (Cl. 252-411) This invention relates to the purification ofcatalysts and more particularly to a method of removing small quantitiesof chlorine from a finely divided platinum catalyst.

As conducive to a clearer understanding of the present invention it maybe pointed out that finely divided platinum catalysts are used forcatalyzing a wide variety of industrial processes. Such catalysts arefrequently prepared on a substratum of inert material such as, forexample, charcoal and may be conveniently prepared by impregnating thecharcoal substratum with a solution of chlorplatinic acid andsubsequently reducing the chlorplatinic acid to metallic platinum infinely divided form on the charcoal substratum.

Platinum catalysts carefully washed after reduction, usually contain arelatively small quantity of residual chlorine that is very difficult toremove. In some processes the presence of this small quantity of inother processes it may be desirable or necessary to remove this residualchlorine in order to carry out the catalytic process efficiently or insome cases to cause the process to proceed at all. To illustrate thetype of process wherein removal of this small quantity of residualchloprepared in this way, even though chlorine has no deleterious efiectbut! time is important reference may be made to co-pending patentapplications of Harold C. Urey and A. V. Grosse Serial No. 466,498,filed November 21, 1942, now Patent No. 2,690,379, and Hugh S. TaylorSerial No. 534,167, filed May 4, 1944, now Patent No. 2,362,227 whichdisclose processes for concentrating the deuterium-containing species inwater by utilizing the hydrogen isotope exchange reaction betweenmixtures of hydrogen and water. In accordance with the processesdisclosed in these applications a countercurrent flow of hydrogen andwater is established in such manner that the hydrogen and water areintimately mixed to cause a transfer of deuterium to take place from thehydrogen to the water. Since the rate of the exchange reaction isrelatively slow it is desirable that the reaction be carried out in thepresence of a catalyst and finely divided platinum on a charcoalsubstratum has been disclosed to be a desirable catalyst.

In carrying out on a large scale the deuterium concentration processesdisclosed in the above-identified applications it is usually desirableto employ process equipment made of copper or copper-containing alloys.In the case of the Taylor process, for example, wherein a hydrogenisotope exchange is effected between hydrogen gas and water vapor, theprocess may be carried out in exchange towers made of copper andconstructed in a manner generally similar to that of the well-knownbubble-cap fractionating tower except that catalyst beds'are located atspaced points within the tower. The mixture of hydrogen gas and watervapor passes intermittently through the catalyst beds to cause thedesired exchange reaction to occur. In the operation of such exchangetowers it has been found that there is a tendency for a small amount ofthe copper of which the tower is made to go into solution and for adeposit of copper to form catalyst. It has been further found that theformation ofthis deposit of copper is attributable to thechlorine content of the catalyst. The precise mechanism of the reaction that occursis not fully understood but it has been definitely established that nosuch copper deposition takes place on the catalyst surfaces in caseswhere the catalyst has been substantially freed from chlorine before thetower is placed into operation.

The removal of such residual chlorine from the platinum catalyst is adifiicult problem. Successive washings with water and/ or treatment withan alkaline solution fail to produce the desired result. In general thechemical reagents that might be expected to work may be said to beeither inadequate for removing this residual chlorine or else react insuch manner as to impair the activity of the catalyst.

It is accordingly an object of the present invention to provide a methodfor removing residual chlorine from a finely divided platinum catalyst.

It is a further object of the invention to provide a method of removingsuch residual chlorine from a platinum catalyst in an efiicient mannerand in a relatively short period of time.

It is another object of the invention to provide a method foreliminating chlorine from a platinum-on-charcoal catalyst which methodmay be temperatures with inexpensive reagents.

Other objects of the invention will be in part obvious and in partpointed out hereinafter.

In one of its broader aspect the. present invention comprises a methodof purifying a finely divided platinum catalyst containing smallquantities of residual chlorine which comprises treating the catalystalternately with dry hydrogen and wet hydrogen until the residualchlorine is substantially completely removed from the catalyst. It hasbeen found that either dry hydrogen alone or wet hydrogen alone iscapable of removing a part of the residual chlorine from the platinumcatalyst but that the rate of removal is excessively slow when eithermaterial is used alone. By treating the catalyst alternately with dryhydrogen and wet hydrogen the time required for removal of the chlorineto the desired extent is substantially decreased. The present method oftreating the catalyst alternately with dry and wet hydrogen is desirablycarried out at an elevated temperature and good results have beenobtained at temperatures as low as 60 C. and as high as C. In generalthe time required to elfect chlorine removal varies inversely as thetemperature. Thus it was found that five alternate treatments with dryand Wet hydrogen are desirably used at 60 C. whereas three suchtreatments sulfice at 110 C.

In order to point out more fully the nature of the present invention thefollowing specific example is given of a preferred embodiment of thepresent method.

Example 1.A stream of pure dry hydrogen was passed through a bed offinely divided platinum catalyst on a charcoal substratum at atemperature of about 110 C. under such conditions as to give a spacevelocity of about 400 mins. (space velocity is defined as the gas flowrate in terms of volume per unit time divided by the volume of thecatalyst bed). The flow of dry hydrogen through the catalyst wascontinued for a period of about two hours and then the dry hydrogen flowwas cut oh? and a flow of wet hydrogen admitted to the catalyst bed.

The wet hydrogen contained a quantity of water vapor such that themixture contained 8 parts by volume of hydrogen to 1 part of watervapor. The temperature of the catalyst bed and stream of wet hydrogenwas maintained at 110 C. and the flow maintained at such a value as togive the same space velocity as that used carriedout at moderate 3during the first step of the process, i. e. a space velocity of 400. Thetreatment with wet hydrogen was continued for a period of two hours andwas followed by a two hour treatment with dry hydrogen under the sametemperature and flow conditions. At the end of this period it was foundthat a suflicient proportion of the residual chlorine.

Duration Grams G1 Cumulaof Treatremoved tive per- Hydrogen used ment inper 100 cc. cent of hours at. chlorine removed that at 60 C.approximately can be removed from the The above table indicates 75% ofthe residual chlorine catalyst using 6 alternate treatments with dry andwet 4}. catalyst" may be used in contact with process equipmentconstructed of copper and copper alloys with no danger of deposition ofcopper on the catalyst surfaces and consequent impairment of theircatalytic activity.

Since many embodiments might be made of the present invention and sincemany changes might be made in the embodiment described above, it is tobe understood that the foregoing description is to be interpreted asillustrative only and not in a limiting sense.

I claim:

1. The method of purifying a finely divided platinum catalyst containingsmall quantities of chlorine which comprises treating said catalyst atan elevated temperature with dry hydrogen, then treating said catalystat an elevated temperature with wet hydrogen having a hydrogen-watervapor volume ratio of about 8:1, and repeating said dry hydrogen and wethydrogen treatments until said chlorine is largely removed from saidcatalyst.

2. The method of purifying a finely divided platinum catalyst containingsmall quantities of chlorine which comprises exposing said catalystalternately for periods of about two hours to streams of dry and wethydrogen at a temperature between C. and C. until said chlorineislargely removed from said catalyst.

3. The method of purifying a finely divided platinum catalyst Containingsmall quantities of chlorine which comprises treating said catalyst withdry hydrogen at a temperature of about 110 C. for a period of about twohours, treating said catalyst with wet hydrogen at a temperature of 110C. for a period of about two hours, and again treating said catalystwith dry hydrogen at about 110 C. for a period of about two hours toremove said chlorine from said catalyst.

References Cited in the file of this patent

1. THE METHOD OF PURIFYING A FINELY DIVIDED PLATINUM CATALYST CONTAININGSMALL QUANTITIES OF CHLORINE WHICH COMPRISES TREATING SAID CATALYST ATAN ELEVATED TEMPERATURE WITH DRY HYDROGEN, THEN TREATING SAID CATALYSTAT AN ELEVATED TEMPERATURE WITH WET HYDROGEN HAVING A HYDROGEN-WATERVAPOR VOLUME RATIO OF ABOUT 8:1, AND REPEATING SAID DRY HYDROGEN AND WETHYDROGEN TREATMENTS UNTIL SAID CHLORINE IS LARGELY REMOVED FROM SAIDCATALYST.